<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        *{
            padding:0;
            margin:0;
        }
        .con{
            width: 400px;
            height: 200px;
            background: #ccc;
            position: absolute;
            left: 50%;
            top: 50%;
            transform: translate(-50%,-50%);
        }
        .con div{
            width: 50px;
            height: 50px;
            background: yellow;
            position: absolute;
        }
        .con div:first-of-type{
            border-bottom-right-radius: 50px;
            left: 0;
            top: 0;
        }
        .con div:nth-of-type(2){
            bottom: 0;
            right: 0;
            border-top-left-radius: 50px;
        }
    </style>
</head>
<body>
<div class="con">
    <div></div>
    <div></div>
</div>
</body>
</html>